Combustion System Using Ammonia as Fuel

This application is a continuation application of International Application No. PCT/JP2023/034734, filed on Sep. 25, 2023, which claims priority to Japanese Patent Application No. 2023-016262 filed on Feb. 6, 2023, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a combustion system using ammonia as fuel.

For example, a combustion system including a gas turbine, a steam turbine, or the like includes a reheating burner in some cases (see, for example, Patent Literatures 1 and 2). The reheating burner heats exhaust gas supplied from a combustor. The heated exhaust gas is used in, for example, heat utilization equipment such as a heat recovery steam generator. With such a configuration, when the temperature of the exhaust gas supplied from the combustor is not high enough for use in the heat utilization equipment, the exhaust gas can be heated up to a sufficient temperature.

Ammonia is known as fuel that does not release CO. Accordingly, it is conceivable that ammonia is used as fuel also in the combustion system including a reheating burner as described above. Furthermore, ammonia is known to have flame retardancy. Accordingly, when ammonia is used as fuel, it is desired to improve flammability of ammonia to improve combustion efficiency.

The present disclosure has an object to provide a combustion system using ammonia as fuel, with which combustion efficiency can be improved.

According to an aspect of the present disclosure, there is provided a combustion system using ammonia as fuel, the combustion system including a combustor, a reheating burner that is in fluid communication with the combustor and that heats exhaust gas supplied from the combustor, heat utilization equipment that is in fluid communication with the reheating burner and that uses heat of the exhaust gas, a re-circulation flow path that supplies a part of the exhaust gas used in the heat utilization equipment to the combustor, and a first heat exchanger arranged on the re-circulation flow path, the first heat exchanger exchanging heat between the exhaust gas and ammonia, the first heat exchanger supplying vaporized ammonia to the reheating burner and supplying cooled exhaust gas to the combustor.

The combustion system may further include a second heat exchanger arranged on the re-circulation flow path, the second heat exchanger exchanging heat between the exhaust gas and liquid ammonia, the second heat exchanger supplying a part of heated ammonia to the combustor and supplying remaining part of the heated ammonia to the first heat exchanger. The first heat exchanger may exchange heat between the exhaust gas and the heated ammonia supplied from the second heat exchanger.

The second heat exchanger may supply the part of the heated ammonia in a liquid state to the combustor.

The second heat exchanger may supply the part of the heated ammonia in a gas state to the combustor.

The combustion system may further include an injector that directly injects liquid ammonia to the exhaust gas flowing through the re-circulation flow path.

The combustion system may further include a denitrification equipment that reduces a nitrogen oxide in the exhaust gas. The first heat exchanger may supply a part of the vaporized ammonia to the denitrification equipment.

According to the present disclosure, combustion efficiency can be improved in the combustion system using ammonia as fuel.

Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Specific dimensions, materials, and numerical values described in the embodiment are merely examples for a better understanding, and do not limit the present disclosure unless otherwise specified. In this specification and the drawings, duplicate explanations are omitted for elements having substantially the same functions and configurations by assigning the same sign. Furthermore, elements not directly related to the present disclosure are omitted from the figures.

is a schematic view showing a combustion systemaccording to a first embodiment. In the present embodiment, the combustion systemis applied to a system including a gas turbine. The combustion systemis not limited thereto, and may be applied to another system including a combustor that can use ammonia as at least a part of fuel. For example, in another embodiment, the combustion systemmay be applied to a system including a boiler that combusts ammonia, and a steam turbine operated by steam generated in the boiler.

For example, in the present embodiment, the combustion systemincludes a tank (ammonia supply source), a pressurizer, the gas turbine, an HRSG (heat recovery steam generator) (heat utilization equipment), an exhaust tower, a first heat exchanger, and a controller. The combustion systemmay further include other components. Furthermore, the combustion systemmay not include at least one of the above-mentioned components.

The tankstores ammonia. Specifically, the tankstores liquid ammonia. The tankis connected to the pressurizerby piping P. The liquid ammonia stored in the tankis supplied to the pressurizerthrough the piping P. The ammonia supply source is not limited to the tank, and may be, for example, other component such as an ammonia producing device.

The pressurizerpressurizes the liquid ammonia supplied from the tank. For example, the pressurizermay be a pump. The pressurizermay communicatively be connected to the controllerby wire or wirelessly, and may be controlled by the controller. For example, the controllercontrols the output of the pressurizerto adjust the flow rate of ammonia supplied from the tank. The pressurizeris connected to piping P. The piping Pbranches out into piping Pand piping P.

The piping Pis connected to the gas turbine. For example, the pressurizersupplies the liquid ammonia to the gas turbinethrough the piping P. In another embodiment, the combustion systemmay include a vaporizer (not shown) on the piping P, and vaporized ammonia may be supplied to the gas turbine.

The piping Pis connected to a reheating burner(described later). For example, a valve Vmay be arranged on the piping P. The valve Vmay communicatively be connected to the controllerby wire or wirelessly, and may be controlled by the controller. For example, the controllercontrols the output of the pressurizerand the opening degree of the valve Vto adjust the flow rate of ammonia supplied to the gas turbineand the flow rate of ammonia supplied to the reheating burner.

The gas turbineincludes a compressor, a combustor, and a turbine.

The compressorcompresses air, and supplies the compressed air to the combustor. The compressed air is used for combustion in the combustor.

The combustorcombusts ammonia supplied from the tank. Furthermore, the combustormay combust mixed fuel of ammonia and other fuel such as natural gas, or may combust only other fuel, depending on situations. The exhaust gas generated in the combustoris supplied to the turbineand used for operation such as power generation.

The turbineis connected to piping P. The piping Pis connected to the HRSG. The exhaust gas used in the turbineis supplied to the HRSGthrough the piping P.

In the present embodiment, the HRSGis provided as the heat utilization equipment that utilizes heat of the exhaust gas. The heat utilization equipment is not limited thereto. For example, other equipment such as a heating furnace may be used as the heat utilization equipment. The HRSGincludes one pipe Por a plurality of pipes Pthrough which water passes. The HRSGheats and turns water into stream by the heat of the exhaust gas. For example, the steam may be used for operation of the steam turbine (not shown).

The reheating burneris arranged upstream of the piping Pin the HRSG, or arranged upstream of the HRSG. The reheating burnercombusts ammonia supplied from the tank(described later). Furthermore, the reheating burnermay combust mixed fuel of ammonia and other fuel such as natural gas, or may combust only other fuel, depending on situations. For example, the reheating burnerheats the exhaust gas when the temperature of the exhaust gas is not high enough to heat and turn water into steam in the HRSG. For example, the reheating burnermay communicatively be connected to the controllerby wire or wirelessly, and may be controlled by the controller. For example, the controllercontrols the heating power of the reheating burnerto adjust the temperature of the exhaust gas.

The HRSGis connected to the exhaust towerby piping P. The exhaust gas used in the HRSGis sent to the exhaust towerthrough the piping P, and is released from the exhaust tower.

Piping (re-circulation flow path) Pbranches from the piping P. The piping Pis connected to an intake flow path of the compressor. Accordingly, the piping Psupplies a part of the exhaust gas used in the HRSGto the combustorvia the compressor. The compressorcompresses mixed gas of air and exhaust gas, and supplies the compressed mixed gas to the combustor.

For example, a valve Vmay be arranged on the piping P. The valve Vmay communicatively be connected to the controllerby wire or wirelessly, and may be controlled by the controller. For example, the controllercontrols the opening degree of the valve Vto adjust the flow rate of the exhaust gas supplied to the compressorthrough the piping P.

The first heat exchangeris arranged on the piping Pand the piping P. The first heat exchangerexchanges heat between the exhaust gas flowing through the piping Pand the ammonia flowing through the piping P. In the present embodiment, the first heat exchangeris of a counter-current flow type in which the exhaust gas and the ammonia flow in directions opposite to each other. In another embodiment, the first heat exchangermay be of a co-current flow type in which the exhaust gas and the ammonia flow in the same direction.

In the first heat exchanger, the liquid ammonia flowing through the piping Pis heated and vaporized by the exhaust gas flowing through the piping P. Accordingly, the first heat exchangersupplies gas ammonia to the reheating burnerthrough the piping P. The reheating burnercombusts the supplied gas ammonia. Gas ammonia has flammability superior to that of liquid ammonia. Accordingly, with such a configuration, the combustion efficiency in the reheating burnercan be improved.

In contrast, in the first heat exchanger, the exhaust gas flowing through the piping Pis cooled by the liquid ammonia flowing through the piping P. Accordingly, the first heat exchangersupplies the cooled exhaust gas to the compressorthrough the piping P. When the temperature of the compressed fluid is reduced, the compressorcan be operated with lower power. Accordingly, with such a configuration, the engine efficiency can be improved.

Furthermore, a conversion NOx value used for regulation is expressed by Expression (1) given below.

Conversion NOx value=NOx concentration measurement value×(atmospheric oxygen concentration−conversion reference oxygen concentration)/(atmospheric oxygen concentration−oxygen concentration measurement value)   (1)

The mixed gas used in combustion in the combustorincludes the exhaust gas supplied by the piping P. The oxygen concentration in the exhaust gas is lower than the oxygen concentration in atmosphere. Accordingly, in this case, the “oxygen concentration measurement value” in Expression (1) described above is reduced, and hence the conversion NOx value can be reduced even when the “NOx concentration measurement value” does not change.

In particular, in the present embodiment, the exhaust gas supplied from the combustoris further combusted by the reheating burner. Accordingly, the oxygen concentration in the exhaust gas supplied to the combustorthrough the piping Pis further reduced by the reheating burner. Thus, the conversion NOx value can be further reduced.

The controllercontrols the whole or a part of the combustion system. The controllerincludes, for example, components such as a processor, a memory, and a connector, and those components are connected to each other via buses. For example, the processorincludes a central processing unit (CPU) or the like. For example, the memoryincludes a hard disk, a ROM in which programs or the like are stored, a RAM serving as a work area, and the like. The controlleris communicatively connected to each component of the combustion systemvia the connectorby wire or wirelessly. For example, the controllermay further include other components such as a display such as a liquid crystal display or a touch panel, and an input device such as a keyboard, a button, or a touch panel. For example, the operations of the controllerdescribed above may be implemented by the processorexecuting programs stored in the memory

The combustion systemas described above includes the combustor, the reheating burnerthat is in fluid communication with the combustorand that heats the exhaust gas supplied from the combustor, the HRSGthat is in fluid communication with the reheating burnerand that uses the heat of the exhaust gas, the piping Pthat supplies a part of the exhaust gas used in the HRSGto the combustor, and the first heat exchangerarranged on the piping P. The first heat exchangerexchanges heat between the exhaust gas and ammonia, and supplies vaporized ammonia to the reheating burnerand supplies cooled exhaust gas to the combustor. With such a configuration, the gas ammonia is supplied to the reheating burner. As described above, gas ammonia has flammability superior to that of liquid ammonia. Accordingly, when the reheating burneruses ammonia as fuel, the combustion efficiency in the reheating burnercan be improved. Furthermore, with such a configuration, the cooled exhaust gas is supplied to the compressor. As described above, when the temperature of the compressed fluid is reduced, the compressorcan be operated with lower power. Accordingly, the engine efficiency can be improved. Moreover, with the above-mentioned configuration, the gas used in combustion in the combustorincludes the exhaust gas supplied by the piping P. The oxygen concentration in the exhaust gas is lower than the oxygen concentration in atmosphere. Accordingly, in this case, the conversion NOx value can be reduced as described above. In particular, in the combustion system, the exhaust gas supplied from the combustoris further combusted by the reheating burner. Thus, the oxygen concentration in the exhaust gas supplied to the combustoris further reduced by the reheating burner. Accordingly, the conversion NOx value can be further reduced.

Next, a system according to another embodiment will be described.

is a schematic view showing a combustion systemaccording to a second embodiment. The combustion systemis different from the above-described combustion systemaccording to the first embodiment in that the combustion systemincludes a second heat exchanger. For other configurations, the combustion systemmay be the same as the combustion systemaccording to the first embodiment.

The second heat exchangeris arranged on the piping Pand the piping P. In the present embodiment, the piping Pbranches out into the above-described piping Pand the piping Pat a position downstream of the second heat exchanger.

In the present embodiment, the second heat exchangeris arranged upstream of the first heat exchangerin the flow of ammonia in the piping P. From another perspective, in the present embodiment, the second heat exchangeris arranged downstream of the first heat exchangerin the flow of exhaust gas in the piping P. The second heat exchangerexchanges heat between the exhaust gas flowing through the piping Pand the liquid ammonia flowing through the piping P. In the present embodiment, the second heat exchangeris of a counter-current flow type in which the exhaust gas and the liquid ammonia flow in directions opposite to each other. In another embodiment, the second heat exchangermay be of a co-current flow type in which the exhaust gas and the liquid ammonia flow in the same direction.

In the second heat exchanger, the liquid ammonia flowing through the piping Pis heated by the exhaust gas flowing through the piping P. In the second heat exchanger, the heated liquid ammonia may be kept in the liquid state or may be vaporized.

The second heat exchangersupplies the heated liquid ammonia or the vaporized ammonia to the first heat exchangerthrough the piping P. The first heat exchangerfurther heats the ammonia supplied from the second heat exchanger. As described above, the first heat exchangersupplies the vaporized ammonia to the reheating burnerthrough the piping P. With such a configuration, the combustion efficiency in the reheating burnercan be further improved.

Furthermore, the second heat exchangersupplies the heated liquid ammonia or the vaporized ammonia to the combustorthrough the piping P. With such a configuration, the combustion efficiency in the combustorcan be improved.

In contrast, the exhaust gas flowing through the piping Pis cooled by the ammonia flowing through the piping Pin the first heat exchangeras described above, and is further cooled by the ammonia flowing through the piping Pin the second heat exchanger. The second heat exchangersupplies the cooled exhaust gas to the compressorthrough the piping P. With such a configuration, the engine efficiency can be further improved.

The combustion systemas described above may provide similar effects to those of the combustion systemaccording to the first embodiment. Furthermore, the combustion systemfurther includes the second heat exchangerarranged on the piping P, wherein the second heat exchangerexchanges heat between the exhaust gas and liquid ammonia, and supplies a part of heated ammonia to the combustorand supplies remaining part of the heated ammonia to the first heat exchanger. The first heat exchangerexchanges heat between the exhaust gas and the heated ammonia supplied from the second heat exchanger. With such a configuration, the second heat exchangersupplies the heated liquid ammonia or the vaporized ammonia to the combustor. Accordingly, when the combustoruses ammonia as fuel, the combustion efficiency in the combustorcan be improved.

Furthermore, in the combustion system, the second heat exchangermay supply the part of heated ammonia in a liquid state to the combustor. With such a configuration, the ammonia is kept in the liquid state from the tankto the combustor. Accordingly, a system of supplying ammonia from the tankto the combustorcan be simplified. In particular, the amount of ammonia used in the combustoris larger than the amount of ammonia used in the reheating burner. Accordingly, the system of supplying ammonia can be more greatly simplified.

Furthermore, in the combustion system, the second heat exchangermay supply the part of heated ammonia in a gas state to the combustor. As described above, gas ammonia has flammability superior to that of liquid ammonia. Accordingly, with such a configuration, the combustion efficiency in the combustorcan be further improved.

Next, a system according to still another embodiment will be described.